Gas-particle partitioning of PCDD/Fs in daily air samples

Eight short-term (24-48 h) air samples were taken at Lancaster, UK, to stud y the gas-particle partitioning of PCDD/Fs. Sampling dates in autumn 1997 w ere selected with a view to minimising temperature fluctuation during the s ampling events. Sigma Cl4-8DD/Fs (Sigma TEQ) for the first 6 samples were 1 .1-3.6 pg m(-3) (15-44 fg TEQ m(-3)), typical of a rural site; two other sa mples had Sigma Cl4-8DD/Fs of 18 and 7.9 pg m(-3), with 320 and 100 fg TEQ m(-3). The observed gas-particle distributions varied from 0-34% particle-b ound for Cl2/3DD/Fs to > 70% for Cl6-8DD/Fs. Measured particle-bound fracti ons were compared to theoretical estimates of their distribution based on t he Junge-Pankow model using three different reported sets of vapour pressur es. The best correlation was obtained using vapour pressures derived from m easured GC-retention time indices (Eitzer and Hites, 1988). Plotting log pa rtition coefficient (K-p) versus log sub-cooled liquid vapour pressure (p(L )) gave excellent correlations with slopes of roughly - 1 for all homologue groups. 2, 3, 7, 8-substituted congeners showed slopes of - 1 for the firs t five sampling events. It is proposed that kinetic factors at the low ambi ent temperatures, coupled with additional emissions during the last samplin g events resulted in non-equilibrium partitioning. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.